Continuous process of producing beryllium fluoride by thermal decomposition of ammonium beryllium fluoride and separate recovery of the constituent fluorides



United rates CONTINUQUS PROCES @F PRODUCING BERYL- LIUM FL'UQRHDE BY THERMAL DECOR IP}- TIQN (ll? AMMQNEUM BERYLLIUM FLUQRIDZE AND SEPARATE REtIU-VERY OF THE CONSTIT- UEN'I FLUORIDES Carl W. Schwenzfeier, Jin, Woodville, Ohio Application December 20, 1955, Serial No. 554,211

3 Claims (CI. 23-88) The invention relates to an improved process of treating ammonium beryllium fluoride in which the double fluoride is subjected to thermal decomposition in a manner to produce beryllium fluoride in a molten state and the ammonium fluoride in a vapor state so that the two constituent fluorides can be separately recovered, the present application being a continuation-in-part of my earlier application Serial No. 231,472, filed June 14, 1951, now abandoned.

The primary object of the invention is to provide a practical and efficient continuous process of producing beryllium fluoride.

A further object of the invention is to provide a process of the character noted which makes possible relatively slow deterioration of the processing apparatus employed and corresponding minimizing of the cost of production.

Another object of the invention is to provide a process which can be carried out with a minimum of health hazards.

With the above stated objects and other more or less ancillary objects in view the invention consists in the series of process steps hereinafter particularly pointed out and claimed.

A preferred specific procedure in carrying out the invention is set forth in the following description with reference to the accompanying drawing which shows apparatus especially designed for practice of the invention, the apparatus being shown chiefly in side elevation but with some parts in section in order to disclose interior construction.

The apparatus, as shown in the drawing, comprises a decomposition furnace which is designated as an entirety by the numeral 1 and has a treatment chamber structure comprising a crucible 2 with dome or cover 3. The crucible rests upon a block 4 formed with a downwardly opening recess. Within the crucible is arranged a conical core 5 which comprises a separately formed annular base 6. The main body of core 5 is fitted with four radial pins 5a the outer ends of which engage the inner side wall surface of the crucible 2 and serve to center the core structure therein. The core has a downwardly opening bottom recess which registers with the central opening in the base 6 to form a chamber 7. In the chamber 7 is arranged a tubular weir 8 which extends through the bottom of the crucible and into the top of the recess of block 4 to afford a discharge from the furnace for molten material. Restricted grooves 6a in the bottom of base 6 afford passageways for molten material from the main chamber of the crucible into the weir chamber 7. Molten material discharged from the furnace may be received by automatic casting means generally designated by the numeral 9, which casting means in turn delivers the cast bodies to a suitable receptacle in housing 10.

The top of dome 3 is apertured to receive a feed tube 11 to which material for treatment is supplied from suitable automatic feeding means of conventional character diagrammatically represented at 12. The side wall of dome 3 is apertured to receive a downwardly inclined 23,819,149 Patented Jan. 7, 195.3

vapor discharge tube 13. All parts of the furnace structure so far described are preferably formed of graphite to afford desirable refractory characteristics both with respect to heat and with respect to corrosive action on the parts by the materials treated.

The crucible of the furnace is surrounded by loose refractory material 14 which rests upon refractory blocks 15, a thin wall of refractory material 16 serving to lateral-1y support the loose refractory material. A high frequency electric heating coil surrounding the furnace crucible is diagrammatically indicated at 1'7, and 18 indicates outer side and top walls enclosing the major part of the furnace crucible.

Closely adjacent to the furnace 1 is a wet-surface condenser and absorber 19 comprising a chambered bottom section 20 and an elongated body 21. The wall of condenser-absorber section 20 is apertured to receive the discharge end of the downwardly inclined vapor conduit 13 of the furnace and the opposite side wall of section 20 is fitted with an access opening 20a in axial alignment with conduit 13 so that a poker can be inserted through the chamber of section 26 to clear the passage of the conduit in case of condensation of solid material therein.

The lower part of condenser-absorber body 21 is fitted with a grid 22 which supports a mass of Raschig rings 23 of refractory material to provide extensive condensing surface. Above the Raschig rings is arranged a multiplechambered distributing weir 24 which receives water or solution from a nozzle 25. The top wall of the condenserabsorber is apertured to receive a vapor outlet conduit 26.

The numeral 2'? designates as an entirety a Cottrell electrostatic precipitator which may be of conventional in terior construction and need not be described other than to mention its typical arrangement of electrodes of one polarity in the form of wires or rods suspended within upright tubes which are of opposite polarity and afford large precipitation surfaces. The precipitator has a vapor inlet conduit 28 with a manifold section 28 a at its upper end to which the vapor outlet 26 of the condenser-absorber is connected, provision being made for the connection to the manifold of two other furnace and condenser.- absorber sets, the manifold connections for which are shown broken away. The conduit 26 has an upward branch 29 with an open upper end controlled by an adjustable damper 3d. The precipitator 27 has a vapor discharge conduit 31 to which the suction inlet of a motor-driven blower 32 is connected, the blower preferably having its discharge (shown broken away) connected to a suitable stack or chimney.

The necessary water or solution circulating means to serve the condenser-absorber and the precipitator comprise a tank 33 which is connected by pipe 34 to motor-v driven pump 35 which elevates the water (or weak solution) to nozzle of the condenser-absorber. A branch pipe 36a connected with pipe 36 supplies water or solution to a spray nozzle 37 of the precipitator 27, the nozzle being arranged to deliver the water or solution on the upper inner surfaces of the above-mentioned tube electrodes. Return pipes 38 and 39 connect the bottoms of the condenser-absorber and the precipitator, respectively, to tank 33. The tank 33 is equipped with a cooling coil 33a for extracting heat from the solution circulated through the condenser-absorber.

In the practice of the invention the preferred procedure is as follows. The broken or crushed ammonium betyla lium fluoride salt, which is to be fed to apparatus 12, is discharged by the latter at a controllable rate into furs nace 1 where the material is heated to decomposition temperature. At the treating temperature, which may be about 900 C., the beryllium fluoride, in molten state, settles to the bottom of the treating chamber in the furnace crucible and, on rising to the level of the upper end of weir 8, is-continu-ously discharged from the furnace to the casting means 9, which in turn discharges the solid cast bodies to a container in the housing 10.

Meanwhile, ammonium fluoride, the other product of 'the decomposition effected in the furnace, is evolved in the vapor phase and withdrawn, by the suction of blower 32, through the discharge conduit 13 into the lower part of the condenser-absorber 19, the downward inclination of conduit 13 having been found a necessary feature of the apparatus to avoid rapid clogging of the conduit and interruption of the continuous operation. The suction effect in the condenser-absorber incident to the operation of blower 32 draws the vaporized ammonium fluoride upward through the wet Raschig rings 23 where the major part of the fluoride is condensed on the cool wet surfaces of the rings and simultaneously dissolved in the wetting water (or weak solution), the solution so formed being displaced by water continuously dripping from the weir 24 to find its way into the lower section 20 of the condenser-absorber and thence, through pipe 38, to tank 33.

The previously mentioned substantially simultaneous condensation and absorption of the vaporous ammonium fluoride which occur on the cold wet surfaces of the Raschig rings of the condenser-absorber are believed to be a substantial factor contributing to the remarkably high degree of recovery which is attained by the apparatus. Prior procedure, in which recovery from the vapor state was carried out by first condensing the vapor to a solid state and then absorbing the solid material, realized a much lower recovery than the present apparatus and method which avoid surface treatment of difficultly wettable solid material.

The arrangement of the condenser-absorber closely adjacent to the furnace is highly advantageous in that the short refractory discharge tube 13 is kept at a sufliciently high temperature by the furnace to substantially avoid solidification of the vaporized fluoride in the conduit. However the temperature of the discharge tube 13 is enough lower than the furnace temperature to reduce some of the ammonium fluoride vapors in the tube to a temperature at which the fluoride is candensed to a molten state. It is because of this that the downward inclination of the conduit 13 is vitally important since it keeps such molten portion of the fluoride flowing in the conduit and thus prevents the clogging of the conduit already referred to. Of course any condensed fluoride that is discharged into the bottom part 20 of the condenser-absorber is dissolved and carried to tank 33. In the event that condensation of vapor occurs in conduit 13, as in case the furnace is at too low a temperature when material is fed into it, the conduit may readily be cleared by inserting a poker through the access opening 20a. If this is to be done during decomposition operation of the apparatus Without escape of fumes from the furnace chamber, the blower 32 should have suflicient capacity so that loss of suction incident to opening the access part 20a can be prevented by closing the damper 3t sufficiently.

A major part of the ammonium fluoride is condensed and dissolved in the condenser-absorber 19 but it is desirable, both from the standpoint of economy and in order to avoid discharge of poisonous material into the atmosphere, to recover as much as possible of such minor part of the fluoride as passes uncondensed through the condenser-absorber. For this final recovery the electric precipitator is well adapted and completes the recovery of all but a very small remnant of the ammonium fluoride, which, in such small quantity, can be discharged into the atmosphere without harmful consequences, especially if it is discharged from a stack at a considerable elevation above the ground. The solid fluoride caught on the collecting electrodes of the precipitator are washed to the bottom thereof by water from the spray nozzle 37 and the resulting solution runs by gravity through pipe 39 to tank 33. It will of course be understood that as concentration of the solution in tank 33 increases it may be drawn off from timeto time for suitable treatment to permit its use for forming more ammonium beryllium fluoride to feed the decomposition furnace. Solution so Withdrawn from tank 33 is replaced with water.

During the above-described operation of the apparatus, as will be understood, a certain amount of air must have access to the interior of the apparatus in order that the suction of the blower 32 may maintain a current from the furnace 1 and through condenser-absorber 19 and precipitator 27 to insure the proper functioning of the condenser-absorber and precipitator. On the other hand it is mandatory that air admitted to the furnace 1 be minimized in order to avoid undue oxidation and destruction of its highly heated graphite walls. Also, it is desirable that the vapors generated in the furnace enter the condenser-absorber at relatively high density so that efiicient action of the condenser-absorber may be realized. A certain amount of air leakage into the furnace 1 through the joints of the furnace treating chamber and through the charge-feeding apparatus is practically unavoidable. Such in-leaking air, which is moderate in amount from the standpoint of oxidation of the graphite parts of the furnace, is combined with the relatively large amount of the ammonium fluoride in the vapor state generated in the furnace and their combined volumes insure a flow of adequate volume through the conduit 13. However, with the condensation of the major part of the vaporized fluoride that occurs in the condenser-absorber there is need for replenishment of the volume of vapor or gas suitable to be passed through the precipitator. Such replenishment, as well as the moderate suction on the furnace, is provided by the branch conduit 29 under the control of the damper 30; for the adjustment of the damper (either manual or automatic) which serves to reduce suction on the furnace to minimize furnace-oxidation and dilution of the vapors entering the condenser-absorber, at the same time provides the ample volume of flow through the precipitator required for its effective operation.

It has been found that the combination of the wet condenser-absorber and the electric precipitator is peculiarly advantageous since the precipitator operates most effectively when vapor introduced into it carries a substantial amount of moisture. Of course there is a tendency for vapor during its passage through the precipitator to pick up some moisture from the wetted surface of the collecting electrode but this action is inadequate; so much so, indeed, that it has been customary to provide separate humidifying means in conjunction with such precipitators. In the present apparatus, the very extensive wetted surfaces within the condenser-absorber 19 afford an exceedingly effective humidifying means for cooperation with the precipitator.

Note has been made in the foregoing description that the coupling of additional furnace and condenser-absorber sets to the same precipitator 27 is contemplated. Such an arrangement is advantageous inasmuch as furnaces such as that illustrated are limited in size where the treating chamber of the furnace is formed of graphite, the crucible and its cover being customarily machined from very large solid graphite cylinders such as are produced for use as electrodes of electro-metallurgical apparatus. 0n the other hand the construction of a precipitator comparable in capacity to that of one of the furnaces is uneconomical and unsatisfactory.

It is emphasized that the downward discharge of the ammonium fluoride from the upper part of the decomposition furnace chamber to the lower section of the condenser-absorber tower 19 is a vital factor in maintaining continuous operation of the process. Without this factor, for the reasons already explained, the conduit 13 would become relatively rapidly clogged by the reduction of the fluoride to a molten or solid state in the conduit. The downward inclination of the conduit hasbeen found effective to keep that portion of the fluoride reduced to a molten state moving through the conduit. It will be apparent that if the conduit 13 were inclined upward instead of downward the molten portion of the fluoride in the conduit would be returned into the treating chamber of the furnace and interfere with the proper and balanced carrying out of the process. The continuous successful operation of the process is also dependent upon the regulated introduction of air into the conduit which connects the upper end of the condenser-absorber tower 19 with the electric precipitator 27. By suitably adjusting the air damper 30 it is possible to achieve both the relatively low suction on the decomposition furnace 1 and the required large volume of air flow between the tower 19 and the precipitator 27. Both of these results, secured by the single air control, are vitally important in carrying out the process. On the one hand, maintenance of a pressure in the decomposition furnace slightly below atmospheric pressure serves both to prevent leakage of noxious fumes from the furnace and to minimize the rate of deterioration of the furnace from oxidization with correspondingly infrequent shutdowns of the apparatus for renewal; and, on the other hand, the supply of an ample flow of air between the absorption tower and the precipitator insures the recovery of substantially all of the ammonium fluoride. The last named result is important not merely from the standpoint of economy but also because it insures a low discharge of noxious material into the atmosphere by the suction fan.

While the procedure and the apparatus which have been n described are such as are preferred, it Will be understood that the invention is intended to cover modifications within the bounds of the appended claims.

What is claimed is:

1. In a continuous process of forming beryllium fluoride, the steps of continuously charging ammonium beryllium fluoride into the closed treating chamber of a decomposition furnace; heating the charge therein at a temperature to decompose the double fluoride and maintain the resulting beryllium fluoride in a molten state and the resulting ammonium fluoride in a vapor state; continuously drawing the molten beryllium fluoride from the bottom of the furnace; continuously discharging the vapors of ammonium fluoride from the upper part of the furnace treating chamber; conducting the so-discharged ammonium fluoride in a continuously downward direction from the vapor discharge opening of the furnace treating chamber into the inlet of a wet-surface condensing and absorbing chamber; withdrawing from the condensing and absorbing chamber the solution of ammonium fluoride formed therein; and continuously maintaining on an outlet of the condensing and absorbing chamber a suction regulated to keep the pressure in the treating chamber of the decomposition furnace slightly below atrnospheric pressure to prevent exit of noxious fumes from the furnace and at the same time minimize the admission of air into the furnace chamber.

2. In a continuous process of forming beryllium fluoride, the steps of continuously charging ammonium beryllium fluoride into the closed treating chamber of a decomposition furnace; heating the charge therein at a temperature to decompose the double fluoride and maintain the resulting beryllium fluoride in a molten state and the resulting ammonium fluoride in a vapor state; con tinuously drawing the molten beryllium fluoride from the bottom of the furnace chamber; continuously discharging the vapors of ammonium fluoride from the upper part of the furnace chamber; conducting the discharged vapors of ammonium fluoride into the inlet of a wet-surface condensing and absorbing chamber; withdrawing the solution of ammonium fluoride formed in the condensing and absorbing chamber; continuously conducting vapors of ammonium fluoride unabsorbed in the condensing and absorbing chamber from an outlet thereof to the inlet of an electrostatic precipitation chamber; continuously subjecting the interior of the precipitation chamber to suction; and admitting air into the conduit connecting the wet-surt'ace chamber and the electrostatic precipitation chamber in an amount regulated to maintain a suction effect, through the wet-surface chamber, on the chamber of the decomposition furnace to keep the pressure therein slightly below atmospheric pressure and at the same time to supply an air current in the conduit between the wetsurface chamber and the precipitation chamber adequate to carry the vapors unabsorbed in the said wet surface chamber into the precipitation chamber.

3. A process as claimed in claim 2 in which the vapors of ammonium fluoride discharged from the upper part of the furnace chamber are conducted therefrom in a continuously downward direction into the inlet of the wetsurface condensing and absorbing chamber.

References Cited in the file of this patent UNITED STATES PATENTS 2,173,290 Adamoli Sept. 19, 1939 2,233,465 Adamoli Mar. 4, 1941 2,490,633 Kawecki Dec. 6, 1949 2,653,856 Barr Sept. 29, 1953 

1. IN A CONTINUOUS PROCESS OF FORMING BERYLLIUM FLUORIDE, THE STEPS OF CONTINUOUSLY CHARGING AMMONIUM BERYLLIUM FLUORIDE INTO THE CLOSED TREATING CHAMBER OF A DECOMPOSITION FURNACE; HEATING THE CHARGE THEREIN AT A TEMPERATURE OF DECOMPOSE THE DOUBLE FLUORIDE AND MAINTAIN THE RESULTING BERYLLIUM FLUORIDE IN A MOLTEN STATE AND THE RESULTING AMMONIUM FLUORIDE IN A VAPOR STATE; CONTINUOUSLY DRAWING THE MOLTEN BERYLLIUM FLUORIDE FROM THE BOTTOM OF THE FURNACE; CONTINUOUSLY DISCHARGING THE VAPORS OF AMMONIUM FLUORIDE FROM THE UPPER PART OF THE FURNACE TREATING CHAMBER; CONDUCTING THE SO-DISCHARGED AMMONIUM FLUORIDE IN A CONTINUOUSLY DOWNWARD DIRECTION FROM THE VAPOR DISCHARGE OPENING OF THE FURNACE TREATING CHAMBER INTO THE INLET OF A WET-SURFACE CONDENSING AND ABSORBING CHAMBER; WITHDRAWING FROM THE CONDENSING AND ABSORBING CHAMBER THE SOLUTION OF AMMONIUM FLUORIDE FORMED THEREIN; AND CONTINUOUSLY MAINTAINING ON AN OUTLET OF THE CONDENSING AND ABSORBING CHAMBER A SUCTION REGULATED TO KEEP THE PRESSURE IN THE TREATING CHAMBER OF THE DECOMPOSITION FURNACE SLIGHTLY BELOW ATMOSPHERIC PRESSURE TO PREVENT EXIT OF NOXIOUS FUMES FROM THE FURNACE AND AT THE SAME TIME MINIMIZE THE ADMISSION OF AIR INTO THE FURNACE CHAMBER. 